Download Optic nerve transection in cats: effect on retinal vessels.

610 Reports
and mean circulation time, Circulation 33: 302,
1966.
6. Laing, R. A.: The photographic eye oximeter:
an instrument for measuring the oxygen saturation retinal blood in vivo. In preparation.
Optic nerve transection in cats: effect on
HERBERT
retinal vessels. PAULHENKIND,
B. GOULD,AND ROY W. BELLHORN.
Unihteral optic lzerue tmnsectiot~without damage to the int~aoculurcirczilation was performed
on thirteen cats. Fluorescein angiogmms, trypsin
digestion, and histologic preparation of the retinas
were carried out. No chatiges itr the retinal circulution and angioarchitecture were observed. These
fitulings were compared to those reported in humans with comparable optic nerue lesions. W e
conclzide that optic nerue transection does not
cause retinal uasciilar alteration, and this fact may
be of pertinence to posterior ocular damage in
glaucoma.
A significant, unanswered question concerning
the pathogenesis of glauconla is the relationship
between increased intraocular pressure and field
loss. Is there primary neuronal damage, or is the
vascular bed initially compromised? C~rcumstantial
evidence exists in support of the latter possibility:
( 1) Kornzweig, Eliasoph, and Feldsteinl demonstrated selective ipsilateral atrophy of the radial
peripapillary capillaries in retinal digest preparations from humans with unilateral glaucoma, and
( 2 ) retinal digest preparations from longstanding
gluacomato~~s
eyes often reveal profound alterations in the vascular bed with prominent capillary
dropout and arteriovenous collateral vessel formation.2 Neither obse~vation,however, proves which
comes first, neuronal degeneration or vascular involvenlent. It is well known that vascular occlusive
disease, i.e., branch or central retinal artery occlusion leads to atrophy of the inner retinal layers.
It has not been demonstrated what effect neuronal
degene~ationhas on the retinal vascular bed.
Our experiment was designed to examine what
effect destruction of the inner retinal layers, by
posterior (retrograde) dcgeneration consequent to
an optic nerve transection, would have on the
retinal vessels.
Materials nnd methods. Twenty domestic cats
were anesthetized with intra~nuscular ketalnine
HCI, 30 mg, per kilogram. After anesthesia occurred, pentobarbital, 15 mg. per kilogram, was
administered intravenously to deepen and to prolong the anesthesia. The cats were placed in dorsal
recumbency and the jaws widely separated. A 3
Fig. 1. A, fluorescein angiogram of right fundus.
B, fluorescein angiogram of same funclus 13 days
after transection of optic nerve.
cm. incision was made into the soft tissue behind
the l a ~ tupper ~nolarparallcl to the midline. Because there is no bony floor of the cat orbit, blunt
dissection allows visualization of the optic nerve
as it emerges from the optic foramen. In 13 cats,
the nerve was carefully dissected free from the
ophthalmic artery and transected posterior to the
point where it is penetrated by the ciliary arteries.
In six animals, both the optic nerve and ~ t sblood
supply were cut. Sham operations involving opening the orbit and d a t i n g the o p t ~ cnerve without
tranbect~onwerc conducted in four animal>. Seventeen cats were subjected only to a unilateral procedure; in thtee cats, a procedute was performed
on both eyes ( I.e., experimental plus sham ).
Ophthalmoscopic examinations were conducted
in all cats befo~eand after optic nerve transection,
m d pre- and postoperative fluorcscein angiography
W ~ performed
S
in five cats.
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Fig. 2. A, retinal digest preparation left eye. B, Retinal digest preparation of right eye, 37 days
after transection of optic nerve. Same animal as Fig. 2, A.
At the ternlination of the experiment, two days
to ten wceks after operation, both eyes were
enuclcated and fixed in formalin. After fixation
the globes were opened and a portion of the retina
removed for trypbin digestion3 with flat mounts
made of the retinal vessel preparations. Routine
histologic sections were prepared from the remaining material and they were stained wit11
hematoxylin and eosin, periodic acid-Schiff reagent, Masson's trichrome, 'won, and myelin stains.
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612 Reports
Fi$ 3. Retinal digest preparation right eye, eight weeks after transection of optic nerve and
ophthahnic artery.
Results. Upon recovering from anesthesia, all
cats having optic nerve transection were observed
to be totally blind on their operated side; they
had ipsilaterally fixed and dilated pupils. Within
two or three weeks most of the animals regained
a consensual reflex in the involved eye and their
pupils returned to almost normal size.
Funclus examination revealed no abnormality of
the retinal vascular bed in those animals only having optic nerve transection. In those with conv
bined nerve and vascular supply transection there
was ophthalmoscopic evidence of markedly diminished blood supply. There was no observable
difference in retinal blood flow comparing the preand postoperative fluorescein angiograms in animals with optic nerve transection (Fig. 1 ) . The
longest postoperative study by angiography was
37 days.
Examination of routine histologic sections revealed alterations only in the eyes with optic nerve
transection. There was loss of the ganglion cellnerve fiber layer in eyes removed four or more
weeks after nerve t~ansection.In one eye removed
ten weeks after surgery, there was marked cupping of the disc. In those cases where both the
nerve and its blood supply were interrupted there
was much more profound inner retinal atrophy,
and deep cupping was obvious at four and eight
weeks. The contralateral control eyes and the
sham-operated eyes were normal.
Analysis of the retinal digest preparations revealed normal angioarchitecture and normal endothelial cell and intran~uralpericyte populations in
both the normal and transected eyes (Fig. 2 ) .
In all instances where both the nerve and the vascular supply had been transected, the digests revealed markedly abnormal angioarchitecture, the
vessels appearing as narrow acellular tubes (Fig.
3).
Discussion. From our results, we conclude that
destruction of the inner retinal layers in the cat,
caused by severing the optic nerve with consequent retrograde neuronal degeneration, does not
significantly alter the retinal vasculature either
anatomically or physiologically. The experiments
were relatively short-term, lasting no more than
ten weeks, and it could be argued that vascular
alterations might take longer to appear. Evidence
from man, however, confirms the general principle
that inner retinal degeneration following upon distant optic nerve damage, without obvious interruption of the retinal blood supply, does not cause
alterations in the retinal vascnlature. For example,
Henkind, Charles, and Pearson4 found a normal
appearing retinal digest in an eye which had been
blind for four months following an episode of
acute ischemic optic neuropathy presumably secondary to giant cell arteritis. In this eye the entire
retinal ganglion cell-nerve fiber layer was absent;
the contralateral eye was uninvolved. Kurz, Ogata,
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Reports 613
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Number 8
and Gross5 reported a case wherein the optic
chiasm had been damaged 13 years previously by
a bullet; there was loss of inner retinal layers, but
the retinal digestion preparation demonstrated no
vascular abnormalities.
While this experiment did not address itself
to the pathogenesis of cupping of the disc, several
points are noteworthy. In cats with both optic
and blood vessel transection there was obvious
cupping evident on histologic cross-sectioning, and
this could be seen by four to eight weeks. In our
longest surviving case, ten weeks, marked cupping
was present even though the optic nerve and
retinal circulation remained intact. Miller0 suggests
that neuronal destruction itself does not induce
cupping, and he presented a case with a flat optic
disc after surgical removal of an optic nerve glioma. Hayreh7 has noted a number of entities associated with cupped optic discs, not all of which
have obvious disruption of the disc or retinal circulation. Whether optic disc cupping can be caused
consistently by neuronal damage alone deserves
further investigation.
It seems likely from available experimental and
relevant clinical data that two statements can be
made: (1) destruction of the vascular supply to
the inner retina leads to degeneration of the ganglion cell-nerve fiber layer; (2) retrograde degeneration of the neuronal elements of the inner
retina does not cause degeneration of the neighboring retinal blood vessels. Thus, if one can
demonstrate retinal vascular degeneration in glaucomatous individuals, it is likely that such degeneration was primary and not a consequence of
the neuronal damage.
Our thanks to Mrs. Mary Ellen Murphy and Mr.
Noel Roa for technical assistance, and to Mr.
Henry Malpica for photography.
From the Department of Ophthalmology of the
Albert Einstein College of Medicine/Montefiore
Hospital Medical Center, Bronx, N. Y. 10461.
Supported in part by National Institutes of Health
Grant No. EY 00613, an unrestricted grant from
Research to Prevent Blindness, and a Fight for
Sight Student Fellowship, Fight for Sight, Inc.,
New York City. Submitted for publication April 28,
1975. Reprint requests: Dr. P. Henkind.
Key words: retinal circulation, optic nerve transection, optic nerve, glaucoma, cats.
REFERENCES
1. Kornzweig, A. L., Eliasoph, I., and Feldstein,
M.: Selective atrophy of the radial peripapillary capillaries in chronic glaucoma, Arch.
Ophthalmol. 80: 696, 1968.
2. Wise, C. N., Dollery, C. T., and Henkind, P.:
The Retinal Circulation, New York, 1971,
Harper and Row, p. 222.
3. Kuwabara, T., and Cogan, D. G.: Studies of
4.
5.
6.
7.
retinal vascular patterns. Part I. Normal architecture, Arch. Ophthalmol. 64: 904, 1960.
Henkind, P., Charles, N. C , and Pearson, J.:
Histopathology of ischemic optic neuropathy,
Am. J. Ophthalmol. 69: 78, 1970.
Kurz, G. H., Ogata, J., and Gross, E. M.:
Traumatic optic pathway degeneration: antegrade and retrograde, Br. J. Ophthalmol. 55:
233, 1971.
Miller, S.: The enigma of glaucoma simplex,
Trans. Ophthalmol. Soc. U. K. 92: 561, 1972.
Hayreh, S. S.: Pathogenesis of cupping of the
optic disc, Br. J. Ophthalmol. 58: 863, 1974.
Vitreous structure. IV. Chemical composition of the insoluble residual protein
fraction from the rabbit vitreous.*
DAVID A. SWANN, IAN J. CONSTABLE,
AND JAMES B. CAULFIELD.
Analysis of the structural proteins in the rabbit
vitreous showed that the hydroxyproline content
was 3.1 per cent w/w compared to a value of
10.9 per cent w/w for equivalent samples obtained
from cattle. In contrast to the discreet fibers in
bovine vitreous, the rabbit constituents occur as
an aggregate of fibrils with a diameter of 15 to 20
A. The amino acid and carbohydrate composition
was similar to vascular basement membrane and
isolated fractions contained significant amounts of
palmitic and stearic acids. The data indicate that
the variability of vitreous structure in different
species is not only quantitative, but also qualitative. It is suggested that in the rabbit the structural proteins may be derived primarily from the
atrophied hyaloid system and that little, if any,
secondary vitreous formation occurs in this animal.
Early studies showed that the principal component of the bovine vitreous fibers was a collagenlike moiety1 and in a later electron microscope
study, Olsen2 was able to prepare segment-longspacing (SLS) aggregates from trypsin-digested
vitreous fibers which showed the same banding
pattern as SLS aggregates prepared from rat tail
tendon collagen. More recently, it was shown that
after extraction with saline and 5M guanidine
hydrochloride, 85 per cent of the "residual protein" fraction from the bovine vitreous was recovered as an insoluble collagenous residue.3 It is
known that both the form of the vitreous (gel or
fluid) and the hydroxyproline concentration vary
markedly in different species. These differences
may be caused by variations in both the type and
amount of collagen present and the extent to
which the collagen occurs together with the other
structural constituents. A preliminary study on
the chemical composition of the rabbit vitreous
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